Northern Hemisphere Heat Extremes in a Warmer Climate: More Probable but Less Colocated With Blocking

• Published in: Geophysical research letters 2023-01, Vol.50 (2), p.n/a
• Main Authors: Narinesingh, V., Booth, J. F., Ming, Y.
• Format: Article
• Language: English
• Subjects: Atmospheric blocking; Blocking; Climate; Climate change; Climatic extremes; Emissions; Extreme heat; Extreme high temperatures; Fluid dynamics; Future climates; Geophysical fluids; global warming; Heat; heat extremes; heatwaves; Historic temperatures; Hydrodynamics; Intercomparison; Northern Hemisphere; persistent weather; Regional variations; Temperature
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL101211

This work uses reanalysis and NOAA Geophysical Fluid Dynamics Laboratory's Coupled Model Intercomparison Project 6 model, CM4, to investigate the colocation of heat extremes and atmospheric blocking in the current climate and an end of 21st century, extreme‐emissions projection. In the present day, the colocation of heat events and blocking is greatest for the strongest heat events. Block‐heat extreme colocation is found to be less prevalent over ocean than land, exhibiting regional variation throughout the Northern Hemisphere. Over North America, colocation is greatest near the northwestern and northeastern coasts, minimizing near the center; over Eurasia, colocation is most prevalent in northern regions. In an RCP 8.5 projection, the historical 90th percentile temperature decreases to 0–70th percentile, depending on the region. This is primarily driven by mean state warming. Blocking is found to decrease along with the colocation of blocking and heat extremes, suggesting that in some regions, the mechanisms driving heat extremes will change in future climates. Plain Language Summary This work investigates extreme heat events and atmospheric blocks (persistent high‐pressure systems), which are known to be strongly linked. The analysis herein shows that the strongest extreme heat events coincide with atmospheric blocks, however, the likelihood of the events being colocated varies from region to region. In a high emissions warming scenario, temperatures exceeding the warmest 10% in the current climate, occur 30%–100% of the time depending on the region. This is mostly driven by an increase in average temperature everywhere—rather than an increase in the variability of the temperature. At the same time, the model predicts that blocking, and the colocation of extremes heat events with blocking, decreases, suggesting the physical drivers of heat extremes will change in a warmer climate. Key Points Blocking is more colocated with heat extremes over land than ocean. Stronger heat extremes are more colocated with blocking End of 20th century 90th percentile temperatures become 0–70th percentile by the end of the 21st century in a high emissions scenario Land heat extreme duration is unchanged in RCP 8.5, but colocated blocking decreases, suggesting changes in dynamics driving heat extremes